... in another; also that the character of the residential districts varies according to the wealth and culture of their inhabitants or the nationality and occupation to which they belong. The city is a coalition of semidetached groups, each of which has a unity of its own. The necessities of work draw all the people together down-town along the lines of streets and railways; now and then the different classes are shaken together in elevators and subways; but when they are free to follow their own volition they flow apart. ... — Society - Its Origin and Development • Henry Kalloch Rowe